Celtics' Rajon Rondo (knee) out for the season

The Celtics announced Sunday that guard Rajon Rondo has torn the ACL in his right knee and will undergo season-ending surgery. ESPN on ABC was the first to report the extent of the injury.

Rondo injured his knee during a 123-111 loss to the Hawks on Friday and did not play on Sunday against the Heat in Boston, with the Celtics initially terming his injury a "hyperextension." The ACL tear was revealed during an MRI on Sunday. ACL injuries generally carry a nine-to-12 month recovery timetable.

Coach Doc Rivers started Avery Bradley and Courtney Lee in his backcourt on Sunday but there's no good way to fill the massive hole left by Rondo's injury. The four-time All-Star was averaging 37.4 minutes per game and he's clearly the most distribution-minded player on Boston's roster.

Bradley, Jason Terry and Leandro Barbosa can pick up some of the ball-handling duties, but they are no replacement for Rondo, one of the best set-up players in the game. For comparison's sake, entering Sunday Rondo had registered more than twice as many assists (420) as Bradley, Terry, Barbosa and Courtney Lee combined (203). Worse yet, Boston's attack has sputtered this season even with Rondo, ranking No. 23 in the league in offensive efficiency. Now what?

The Celtics, one of the league's biggest disappointments in the first half of the season, are 20-23 and sit in the No. 8 seed in the Eastern Conference playoff race. Boston has qualified for the playoffs in five straight seasons, advancing to the Eastern Conference finals last year, but sits just two games up on the Sixers for the final playoff spot.

Celtics president Danny Ainge, always active around the trade deadline, must ask himself whether he's staring at a lost season.

Rondo, 26, is averaging 13.7 points, 11.1 assists, 5.6 rebounds and 1.8 steals per game this season. His assist numbers are league-leading for the second consecutive season. Earlier this month, he was voted as a starter for the Eastern Conference in the 2013 All-Star Game.